Help needed machining ends of leadscrews

Hello

I need to turn shoulders on the ends of 3 leadscrews for a homemade CNC machine. Even the shortest of the 3 leadscrews, at 750mm (the largest being 1120mm), is to large to turn on the 7 x 12 mini lathe I have in my workshop.

If any members in the London area think that they have a machine up to the task or can recommend a local firm that undertakes small jobs like this I would love to hear from them. I'm happy to reimburse for work done or swap for machine time on my Denford Triac CNC machine. Alternatively if anyone has had success supporting long stock on a 7 x 12 mini lathe then I would be interested to hear how to do it.

Many thanks in advance

Hello Rupert,

For some reason I don't understand I can't attach pictures to replies like this any more, the submit button has vanished, but if you look in my albums under the topic of drilling long bars you will see how I did that work on my Myford.

I have a vertical slide which allowed me to centre the bar in front of the chuck, the remote end of the job was carried in a fixed steady with the tailstock taken off the bed. Feed was by moving the job towards the chuck. The concept might give you some ideas. I would help but I live in North Yorkshire.

Brian

Edited By JasonB on 01/02/2016 19:44:07

Can;t you do what capstan operators do and hold the stock in the chuck with the length hanging out of the back of the spindle bore with it rotating on/in a bearing held in an outboard support?

Frank

Probably won't fit down a minilathe spindle bore. What dia are your leadscrews as it will be helpful for any one offering if it will fit down the spindle.

As brian said you could hold the work stationary and use a boring head set to cut the external diameter as you feed the work towards the chuck

Edited By JasonB on 01/02/2016 19:42:45

Think a mini lathe would seriously struggle to get thru or under the case hardening on a ball screw.

Some of them are hardaswitchestits.

Also if you have say the popular 16mm screws and want to do down to 12 or 14mm chances are they won't clean up and you have lumps in the surface as it mimics the thread.

Best to grind to size if these are the sizes you want.

Thanks very much to everyone who took the trouble to respond. Brian, that setup is really clever. Thank you for posting the photo it showed up in the thread just fine. Jason, the 750mm leadscrew has a diameter of 12mm which I'm hoping to turn down to 10mm at both ends. The larger leadscrews (1120mm and 1050mm respectively) are both 19mm in diameter and need to be reduced to 15mm at both ends. Frank, thank you the set up you suggested is exactly what I initially considered and is probably what I will end up doing if I can't find someone locally with a much larger machine. John, I did a test cut with the smaller leadscrew sticking out of the outfeed and poorly buttressed with a bodged together support. The results weren't great but it's difficult to say whether that was due to chatter from the flimsy support or the hardness of the steel.

Thanks again for the replies. I really appreciate the help.

thanksI have been planning a similar Cnc leadscrew turning operation. What is stopping me at the moment is that I can't work out how to ensure the leadscrew is concentric in the lathe. Given that it is threaded (in my case anyway) for its whole length, where / how do you apply a dti gauge? Any ideas gratefully received.

Have a sacrificial part on the end of the leadscrew, so you can do all the cutting work at the chuck end.

Use a fixed steady, as above, but jam the leadscrew into a bearing, and fit the bearing inside the fixed steady, held by the fingers, this lets the long bit spin freely in the fixed steady while you work

I used old bearing, from a car garage scrap bin.

Its fiddly, but works if you can do it

Don't run it up to 2000 rpm btw, a few hundred or less max IMO

Edited By Ady1 on 01/02/2016 22:21:30

For setting up with DTI turn a sleeve to slip over the threads, anything quick and easy plastic/aluminium etc.

If you have a little excess length on the leadscrews, just chuck the end. Support the screw with a steady rest at the end of the lathe bed. If the pitch is too coarse to use the steady directly on the screw, use a sleeve or cat head in the steady. Turn down the diameter and face the shoulder. Cut odd the end you had in the chuck.

Hi Rupert

where in London are you, if you are SW then I may be able to help.

Trevor

Hi Rupert - welcome to the forum (or at least posting).

I machined a smaller ball screw recently, which as John said was hard and as tough as old boots. Tipped tools are definitely needed and a mini lathe isn't going to give you what you want no matter how you set it up in my opinion.

I held mine in the chuck and turned it conventionally, but I couldn't clock it accurately, even with a large flat end on the dial gauge. Nor was there a centre hole in the end, which would have sorted it.

So in the end I set up my griptru chuck spot on with a dowel of the same diameter and just went for it.

End result was good and there is no hint of any run out in use.

Cheers - Will

It's a bit late now that the horse is bolted but when if buy your leadscrew (ballscrew and ballnut?) from a famous Chinese site, many of the suppliers will machine the ends to your drawings for only a fiver extra. I did this with mine and they came out very well including keyways, shoulders and threads at both ends. My ballscrews were 25mm dia and the longest one was almost 1.5m long so little chance of fitting in the Bantam.

Worth thinking about if you are planning to get some.

I did this operation with a Myford S7 2 years ago so:

A few observations.

1. The machined end does not have to be exactly concentric as you will be using some kind of coupling between the drive motor and the lead screw. Get it a good as you can though.

2. I machined up a tapered plug bored to the outer diameter of the lead screw to support the end that protruded through the head stock.

3. You could consider machining a press fit bush or loctite similar to the end and do all your machining on that bit.(before attachment obviously).

regards Martin

Great idea.

Jason B,

Thank you for posting the picture for me, the restriction I am experiencing is really frustrating. I have to say the whole process is clanky in the extreme and I would have thought that clicking the OK button might have been sufficient.

The Submit button was often difficult to get to stuck out on the extreme right---it is now completely off screen.

Anyway, the idea has promoted some useful responses

Brian